Recent years have seen some remarkable progress in liquid crystal technology, as well as progress in improvements to angle of visibility, responsiveness, etc., which long had been identified as problems to be solved. Correspondingly, applications of liquid crystal display devices also extend to large-sized televisions. However, even at the present time, when liquid crystal response characteristics have been improved, moving images displayed on liquid crystal televisions occasionally appear blurry.
Liquid crystal display devices do not provide self-light-emission displays, but provide non-self-light-emission displays by adjusting light transmittance of a liquid crystal panel through voltage. In liquid crystal display devices, video data for one frame is written onto each pixel of the liquid crystal panel, and the pixel holds voltage for video data written earlier until video data for the next frame is written. This allows liquid crystal display devices to provide a hold-mode display in which video is held over one frame period. It is generally known that a blurry moving image (hereinafter, referred to as a “moving image blur”) appears on a display device for providing a hold-mode display due to the viewer's following line of sight. Liquid crystal display devices have so far been disadvantageous in terms of image tailing due to a slow liquid crystal response speed (one frame period or more is taken). However, in recent years, the liquid crystal response speed has been improved to be within one frame period, and correspondingly, any moving image blur caused by providing a hold-mode display is acknowledged as an issue.
In CRTs, unlike in liquid crystal display devices, each pixel is irradiated with a beam for a certain time period within one frame period, and emits light while being irradiated with the beam. This allows CRTs to provide an impulse display in which each pixel emits light for a short time period within one frame period. In display devices for providing an impulse display, after emitting light once, pixels do not emit light until the next frame period, and therefore any moving image blur appears due to following line of sight (but, tailing might occur due to afterglow).
Therefore, a conceivable method for alleviating any moving image blur on liquid crystal display devices is to provide a pseudo-impulse display in liquid crystal display devices as in CRTs. Concretely, known methods are to cause a backlight to blink for a time period within one frame period or to provide a black display for a time period within one frame period. In addition, another known method for alleviating any moving image blur is to provide an increased display frequency by frame interpolation (Non-Patent Document 1).
Among the above, the methods that provide a pseudo-impulse display (the backlight blinking method and the black display method) have a problem where brightness and contrast of the liquid crystal panel might decrease, resulting in flickers by impulse display as in CRTs. Accordingly, it might be said that the frame interpolation method free from such a problem is superior as a method for alleviating any moving image blur.
As for frame interpolation, the following techniques are known. Patent Documents 1 and 2 disclose methods in which one frame is divided into a plurality of blocks, a block-by block matching process is performed to obtain a motion vector, and the blocks are moved by an amount equivalent to ½ times the obtained motion vector, thereby generating an interpolation frame. Patent Documents 3 and 4 disclose methods in which motion vectors are obtained for a plurality of block sizes, and an optimum motion vector is selected from among them. Patent Document 5 discloses a method in which frame interpolation is used to perform frame rate conversion at various rates.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 3-263989
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2-206991
[Patent Document 3] Japanese Laid-Open Patent Publication No. 1-192273
[Patent Document 4] Japanese Laid-Open Patent Publication No. 6-153185
[Patent Document 5] Japanese Laid-Open Patent Publication No. 2005-148521
[Non-Patent Document 1] Ishiguro and Kurita, “Consideration on Motion Picture Quality of the Hold Type Display with an octuple-rate CRT”, the Technical Report of the Proceeding of the Institute of Electronics, Information and Communication Engineers, EID 96-4, Jun. 7, 1996, Vol. 96, No. 87, pp. 19-26